The present invention relates to coking oven constructions, and more particularly to an arrangement for providing a draft control in a coking oven construction.
The distillation gases and vapors which leave the coking oven chambers through the outlet conduits are usually collected in a collecting conduit, extending as a rule over the entire length of a battery of coking ovens. The gases must be cooled from their oven temperature of approximately 650.degree.C to a much lower temperature of approximately 100.degree.C. The purpose of providing the collecting conduit is to make it possible to mix, compensate and cool the differential amounts of gas which rise from the different coking oven chambers, and to eliminate as much as possible of the tar which is present in these gases.
The pressure existing in this collecting conduit is of great importance for the proper operation of a coking oven. As a rule, the gas is withdrawn from the coking oven in such a manner that a slight overpressure exists in the collecting conduit ahead of the draft control or throttle flap, to the extent of approximately 3-7 mm water column. The pressure which is required is selected and maintained by a regulating device which operates the throttle flap that is located at the beginning of each suction conduit communicating with the respective coking oven chamber.
As a general rule, the gas is withdrawn behind the throttle flap at a suction of approximately 100 mm water column, and it is clear from this that at this pressure differential the largest part of the suction conduit cross-section can be closed by a fixedly mounted blocking member, and that for purposes of effecting the regulation of pressure in the collecting conduit it is usually sufficient to install a relatively small throttling flap in this blocking member and which usually covers the approximately 15% of the total cross-sectional area of the suction conduit that is not blocked by the holding member. However, this involves certain disadvantages which have not yet been solved in the prior art. In particular, the requirements which are made of the accuracy of pressure regulation in the collecting conduit are very high, since a pressure which exceeds atmospheric pressure by only a few millimeters water column is to be maintained and, moreover, is to be maintained in such a manner as to be free of fluctuations over the entire coking period. The type of throttling flap heretofore used can meet this requirement only when it is in a certain position, or in a certain range of positions, approximately at a 45.degree. open position. Assuming that the amount of gas flowing into the collecting conduit increases, which occurs quite frequently in operation of the coking chambers, then the throttle flap moves into or close to the "closed" position. When this takes place, a fluctuation-free regulation of the pressure in the collecting conduit is no longer possible, and the pressure in this conduit can then fluctuate by approximately .+-. 5 to .+-. 7 mm water column from the desired overpressure of, for instance, 3 mm water column. On the other hand, if the amount of gas flowing into the collecting conduit is substantially increased, for instance when preheated coal is introduced into the coking chambers, then the free cross-section of the conduit that can be exposed by the prior-art throttling flaps is no longer sufficient -- even when the flap is in its fully open position -- to permit the increased amount of gas to pass without causing an increase of the pressure in the collecting conduit.